1. Field of the Invention
The present invention relates to circuit testing devices and methods and, more particularly, to such devices and methods for radio-frequency circuits.
2. Description of Related Art
Test probes for use in testing electronic circuitry are known in the art to comprise one or more elongated arms having a downwardly depending, typically pointed, electrically conductive distal tip for contacting a portion of the circuit. One of the inventors of the present application has disclosed test probes and assemblies in U.S. Pat. Nos. 4,151,465; 4,177,425; and 4,618,821, the contents of which are incorporated herein by reference.
It is known to be preferable for the probe arm to have a certain amount of flexibility for permitting reproducible and nondamaging contact with the circuit. Exemplary flexure means are disclosed in the ""465 and ""821 patents. Other such probes are disclosed in U.S. Pat. Nos. 4,973,903; 4,965,865; 5,720,098; and 5,883,519.
It is therefore an object of the present invention to provide a probe for testing circuits having improved flexibility.
It is a further object to provide such a probe having a longer lifespan and durability.
It is another object to provide such a probe having a tunable bandpass.
It is an additional object to provide such a probe having a controllable impedance.
It is also an object to provide such a probe that functions in the gigahertz rf range.
It is yet a further object to provide a method of making such a probe.
It is yet another object to provide a method of using such a probe.
These and other objects are achieved by the present invention a test probe for testing microcircuits. The test probe comprises a unitary elongated electrically conductive arm member that is movably affixable to a retaining block. The test probe has a pair of generally planar and parallel side surfaces extending along a longitudinal axis. A rear end portion is for connecting to a test circuit, and a front end portion is for contacting a circuit to be tested and comprises an upwardly extending tip.
A rear central portion is positioned adjacent the rear end portion, with the front central portion between the rear central portion and the front end portion. The front central portion has a slot extending through the arm between the side surfaces.
Typically the test probe is sandwiched in spaced relation between two similarly constructed ground probes, these having rear portions for connecting to ground. These three probes are movably affixed to a retaining block having slots therein for holding the probes.
It should be emphasized that the present invention has great adaptability for different situations. For example, the assembly may have one or more contact points depending upon the application. The assembly may also be configured as a probe where it is moved from contact point to contact point, such as for use as a semiconductor wafer probe. It may additionally be configured as a socket where multiple contact points are arranged in a pattern and a device is inserted or placed onto the contact points.
A particular benefit of the present invention lies in its multiplicity of degrees of freedom, including selectable impedance, selectable contact spacing, selectable overtravel, selectable contact pressure, and selectable frequency response.
Most probes that are currently available are designed for a characteristic impedance of 50xcexa9, with 75-xcexa9 probes also available. With the present invention, a range of impedances is achievable as a function of geometry, by adjusting the shape of the contact and the proximity of the adjacent ground contact or reflecting structure in concert with the dielectric between them controlling the impedance.
In addition, the contact spacing is adjustable for each application.
Overtravel is the ability for the contact(s) to be moved beyond an initial point of contact with a device. The type, thickness, and shape of material used for the contact controls overtravel. It is believed desirable to have an abundance of overtravel and strict control of it because: (1) Overtravel provides the ability to planarize an array of contact and eliminates the need for ultraprecise orthogonal relationships between each contact and between the contact array and the device to be tested; and (2) the shape of the contact and overtravel creates a torsion component that controls the contact pressure applied to the device being tested.
The probe assembly of the present invention is designed for very wide frequency response, from dc to hundreds of gigahertz (1010 Hz). The response can also be tailored to fit the requirements of a given application by limiting the high-, low-, or mid-frequency response by changing the shape, dielectric material, and contact-to-contact proximity.
The spacing, impedance, overtravel, and frequency requirements of the application dictate the materials used and the final shape of the contact or contact array. The contact is designed iteratively, with an initial shape selected to fit the physical spacing, overtravel, and pressure constraints. A dielectric is chosen based on the shape selected to obtain an impedance close to the design requirements. Multiple dielectrics may be required to maintain the desired impedance from end to end of the contact. Mathematical simulations are performed and the results evaluated. Adjustments may be made as needed to optimize the response, and simulations run again if necessary until a desired simulation is achieved. The resulting design is manufactured and tested and redesigned if the simulated and actual results are not comparable to a desired degree.
The features that characterize the invention, both as to organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawing. It is to be expressly understood that the drawing is for the purpose of illustration and description and is not intended as a definition of the limits of the invention. These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawing.